Multiple offset
Illustrate, please, including what you start with, the User steps and inputs, and the end result.
The extraordinarily difficult part about that is what needs to happen along the offset results where a change in the central Polyline path direction occurs. With bends between line segments [as it looks like in your image], the location of a vertex in a result Polyline will be short of the vertex in the central path if the Polyline bends toward the side of the result, or beyond it if it bends away, and how far short or beyond will be a function of a combination of the offset distance and the angle of the change in direction, with some trigonometry involved. So a routine would always need to be looking ahead to the Polyline segment beyond the one it is trying to draw parallel to at the time.
And questions arise: Would the path Polylines ever involve any arc segments? If so, would they always and only have tangent transitions at their ends, whether joining line or other arc segments? [If they would always be tangent transitions, and if there would never be corner bends with line segments on both sides, the great difficulty described above would be removed, but the arc segments themselves make for line-vs.-arc-mode complications for the result Polylines.]
Need to do a offset then trim to vertical ends maybe use Fillet. Joining segments as you go. Like Kent not a easy task.
